50 SEA-SHORE LIFE 
They have no spines and their skeleton is often reduced to minute 
anchor-shaped spicules within the skin. The mouth is at one end 
of the worm-shaped body, and is surrounded by feathered or 
branching tentacles. In some species there are five double rows 

Fig. 24; Variations of the COMMON STARFISH. 
From Long Island Sound. 
of tube-feet down the sides of the body, but in others these are 
absent. When disturbed sea cucumbers have the curious habit of 
casting out their viscera, and afterwards regenerating them. They 
are sluggish creatures, and either live within the sand or under 
rocks or crawl slowly over the bottom, feeding upon minute organ- 
isms that are contained in the sand or mud which they swallow. 
Sea urchins or Hehini may be compared to starfishes without 
arms. They are usually provided with a skeleton made for the 
most part of six-sided plates fused or rigidly joined together. 
They have five sharp-edged teeth with which they gnaw off minute 
